Lower Palaeozoic plankton: PRESIDENT’S ANNIVERSARY ADDRESS 1964

摘要: The graptolite biocoenosis is accepted as the epipelagic or oceanic plankton fauna of Lower Palaeozoic, although geosynclinal deposits in which remains occur are not typically oceanic. Local variation within geosynclines implies a measure permanence and stability their faunas, but general similarity successions calls for frequent intercommunication, probably drifted into seas from outlying areas. location these oceans introduces problem continental drift. Reconsideration morphological evidence suggests that nema (or virgula) attachment was exception adult graptoloid may have been more prevalent juvenile stages; occurrence ‘size limit’ stages with prominently developed could prove functionally significant. Some form vacuolated extrathecal tissue seems most plausible alternative buoyancy mechanism forms. There some (adult) Tremadocian dendroids, origin Graptoloidea be causally related to phase development Sargasso-like seas. Other constituents briefly reviewed; few organisms appear acceptable principally algae (including filamentous blue-green hystrichosphaeres), radiolaria, coelenterates (various medusae, siphonophores, ? ctenophores), small inarticulate brachiopods, conodonts, possibly certain trilobites, orthoconic nautiloids. suggestion graptolites lived at various depths accepted. Temperature, however, might well affected geographical distribution. Nemagraptus gracilis Monograptus turriculatus range nearly 40° s about 75° n, if latitudes indicated by palaeomagnetic evidence, both approximate closely warm-temperate tropical zone. Relation ‘pre-continental drift’ positioning Americas anomalies. Further work on distribution-patterns individual species provide presence an early Atlantic Ocean; failing this, central parts would only indication regions (other than Pacific) throughout Palaeozoic.